In the last 16-17 years of getting to know Dream Theater and Mike Portnoy's music, I've kind of grown accustomed to his play style, and could probably pick it out in a line-up if I needed to, but that doesn't mean his fills and grooves are boring for me. He is the kind of drummer who definitely tries his hardest to play to serve the music, and sometimes that means going back into his memory and using certain tools and tricks to lay down a groove or fill that sounds right to him.
He's got strong personality in the studio, but I don't think he'd argue to keep his takes if the other members of whatever band he's recording with weren't happy with what he did. In the end, he is a music fan as much as he is a musician, so I'm sure he wants to serve the song more than anyone else.
In the last decade or so, whenever a new album comes out with Mike on it, I listen to his drum parts carefully to pick out the parts I feel are NEW or DIFFERENT for him, grooves that I've never heard him do (for example, parts on Neal's Momentum album, or the Kaleidoscope album by Transatlantic), or crazy fills he's not done before (The Whirlwind is chock full of them), and it makes it like a fun little egg-hunt to find the stuff that makes that album unique, as far as Mike's playing goes.
I will agree, though, that because of the frequency at which Mike releases new music each year, if you're a fan of all of them, you might burn yourself out on listening to his drumming. Thankfully, I'm not a big fan of his strictly-metal stuff, and I've not really listened to SOA and TWD very much over the last few years, so most of my new-Mike-music intake is mostly from his work with Neal Morse, and if I'm not bored with Neal's over-use of certain musical ideas, I'm definitely not going to get bored with Mike's!
-Marc.